Adds __rmul__ to collections.deque (RustPython#2844)

* Adds `__rmul__` to `collections.deque`, refs RustPython#2834

Author: sobolevn

Lib/test/test_deque.py

@@ -355,8 +355,6 @@ def test_insert_bug_26194(self):
             else:
                 self.assertEqual(d[i-1], 'Z')
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_imul(self):
         for n in (-10, -1, 0, 1, 2, 10, 1000):
             d = deque()
@@ -388,8 +386,6 @@ def test_imul(self):
             self.assertEqual(d, deque(('abcdef' * n)[-500:]))
             self.assertEqual(d.maxlen, 500)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_mul(self):
         d = deque('abc')
         self.assertEqual(d * -5, deque())
@@ -1003,11 +999,11 @@ def test_subscript(self):
     def test_free_after_iterating(self):
         # For now, bypass tests that require slicing
         self.skipTest("Exhausted deque iterator doesn't free a deque")
-    
+
     @unittest.skip("TODO: RUSTPYTHON TypeError: unexpected payload for __eq__")
     def test_pickle(self):
         pass
-        
+
     def test_iadd(self):
         pass
 

vm/src/stdlib/collections.rs

@@ -303,14 +303,16 @@ mod _collections {
         }
 
         #[pymethod(magic)]
+        #[pymethod(name = "__rmul__")]
         fn mul(&self, n: isize) -> Self {
             let deque: SimpleSeqDeque = self.borrow_deque().into();
             let mul = sequence::seq_mul(&deque, n);
-            let skipped = if let Some(maxlen) = self.maxlen.load() {
-                mul.len() - maxlen
-            } else {
-                0
-            };
+            let skipped = self
+                .maxlen
+                .load()
+                .and_then(|maxlen| mul.len().checked_sub(maxlen))
+                .unwrap_or(0);
+
             let deque = mul.skip(skipped).cloned().collect();
             PyDeque {
                 deque: PyRwLock::new(deque),